This invention relates to an improvement in block pattern provided on the ground-contacting portion of a tire. More particularly, the present invention is concerned with a pneumatic radial tire for passenger cars improved with respect to control stability on dry roads, control stability on wet roads and comfortableness in riding.
In recent years, with the development of networks of expressways and improved performance of passenger cars, more and more strict and various performance requirements have been applied to tires. For example, there have been proposed all season tires of which the traveling performance on wet roads is not very poor as compared with the traveling performance on dry roads and tires wherein a special belt material is used for improvement in the comfortableness in riding.
Meanwhile, it is known that since traveling performance on dry roads (dry control stability), traveling performance on wet roads (wet control stability) and comfortableness in riding interfere with each other, the improvement in one of the performances causes lowering in the other performances. Hitherto, tires meeting all the above requirements have not been proposed.
Accordingly, the present inventors have made various studies for simultaneously improving all of the above performance requirements. As a result, the present inventors have noted that (1) the control stability are mainly evaluated during cornering and (2) the comfortableness in riding is mainly evaluated during traveling on the straight. Further, in studying the functions of the block pattern of the ground-contacting portion of the tire, the present inventors have closely examined how the functions of the tires can be optimized under such conditions that the tires have been mounted on a vehicle, as opposed to the conventional method in which examinations were made using tires alone. Particularly, with respect to flat tires having a flatness ratio of 0.7 or less which has been used in recent years, it has become possible to disperse the functions of the ground-contacting portion of the tire in respective portions responsible for the function, because a large radial width (ground width) can be adopted. In other words, attempts have been made on the optimization of all the situations by maximizing the functions each associated with the performance which appears to be the most important under a certain situation.